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Chapter 2
WATER CIRCULATION PATTERNS BETWEEN
UNIVERSITY AVENUE AND ASHBY AVENUE
Linda Goad
Introduction
The purpose of this study is to determine a general water circulation pattern
for the surface waters in and around the embayment between the Berkeley Marina and
Emeryville Marina (see map, page vi). This area was chosen because it is part of a
proposed East Bay Shoreline Park that is being considered by the State Department
of Parks and Recreation and the State Coastal Conservancy, and because there is a
proposal to develop a beach between Ashby Avenue and University Avenue. Water
circulation patterns need to be studied in order to determine what effects they
will have on the stability of the proposed beach.
This study area is part of the complex San Francisco Bay estuary. Water
circulation in estuaries differs from that of the open ocean, and a few general
properties will be discussed below.
General Properties of Estuarine Water Circulation
Estuaries are dynamic entities. The ebb and flow of waters from the ocean
meet and mix with the fresh waters draining from the land. There are many defini
tions for the term "estuary," but the most commonly accepted is that of Pritchard:
"An estuary is a semi-enclosed coastal body of water which has a free connection
with the open sea and within which sea water is measurably diluted with fresh
water derived from land drainage" (1967, p. 3).
Many physical processes affect the behavior of an estuary, including tidal
influence, river inflow, and wind action. The waters are mixed primarily by tides;
the river discharge produces a net outflow of these waters, thereby flushing the
estuary (McCulloch et al. , 1970). In San Francisco Bay., river inflow and wind are
also major causes of mixing (Conomos, 1979).
Estuaries can be classified in a number of ways depending on geometric and
bathymetric configuration, physical oceanographic characteristics of circulation
and mixing, or both. If estuaries are classified by their circulation patterns,
- 55 -
the cause of the water motion is used as the classifying principle. The three main
causes are the wind, the tide, and the river.
Pritchard (1955) classified estuaries based on the advection-diffusion equation
for salt which states that the time rate of change observed in the salinity at a
fixed point is caused by two different physical processes—advection and diffusion.
Advection leads «to a mass flux of water as well as a flux of salt, while diffusive
processes are associated only with a flux of salt. The advective processes are
associated with the net circulation pattern, and the diffusive processes with
turbulent or eddy mixing. A classification is derived by grouping together all
estuaries in which the changes in salinity are produced mainly by the same causes.
With this kind of classification, there is a sequence of estuarine types with a
different circulation pattern; any estuary may pass through this sequence as condi
tions change.
Estuaries can be classified into four main types, ranging from the highly
stratified salt wedge estuary to the well mixed, vertically homogeneous estuary
(Pritchard and Carter, 1971). The Type A, or salt wedge, estuary belongs to the
river-dominated category and is highly stratified. The Type B, or partially mixed
estuary, is sufficiently influenced by the tide to prevent the river from dominat
ing the circulation if the volume flow of the tidal oscillation is much greater than
the volume flow of the river. The salt wedge is erased by the added turbulence
of the tidal flow; salt water is mixed upward and fresh water is mixed downward.
The difference between the surface and bottom salinities remains substantially
constant over the estuary. In a Type C estuary, tidal velocities are further in
creased, and the water becomes vertically homogeneous. A Type D estuary is one
in which the tide is so large in relation to the river that it almost overwhelms
the effect of the river flow. This is a sectionally homogeneous estuary, in which
the salinity is homogeneous both laterally and vertically (Pritchard and Carter,
1971).
Factors Affecting Nearshore Circulation of Estuaries
Several factors affect the pattern of nearshore circulation in estuaries. These
include the effects due to tides and tidal currents, wind currents, longshore cur
rents, flushing by rivers, and various obstructions.
Tides are movements of the oceans set up by the gravitational effects of the
sun and moon in relation to the earth. Tides are important in estuarine geo-
morphology because currents are generated as the tide ebbs and flows. Tides move
- 56 -
in harmony with the gravitational forces of the sun and the moon, and their effects
are seen most strongly in shallow and relatively enclosed ocean areas (Bird, 1968).
Currents can also be generated by the wind. When wind blows over water, it
tends to drag the surfact particles of the water along with it. Thus, the water
surface acquires a motion in the direction of the wind, although the velocity of
the water never equals that of the wind (Johnson, 1965). In an estuarine system,
tidal currents predominate under normal weather conditions, but strong winds and
freshets can bring about nontidal currents, which can modify considerably the speeds
and directions of the tidal currents. Currents generated by wind and tide can be
strong enough to move surficial sediment on the sea floor. Relatively weak currents
can transport sediment in the nearshore zone (Bird, 1968). Currents are also re
sponsible for the various kinds of ripple patterns on tidal flats and on the floors
of estuaries.
Longshore currents play an important part in the longshore movement of material,
thereby contributing to the formation of many coastal features. The volume and
velocity of river flow also plays an important part in determining where the fresh
water and salt water will mix. The relative strengths of the river flow and the
tidal flow are primarily responsible for the net nontidal estuarine circulation pat
tern. This net nontidal circulation is important in determining the rate of in
filling of most estuaries (Schubel, 1971).
Points, breakwaters, and piers all influence the circulation pattern and alter
the direction of the currents flowing along the shore. Generally these obstructions
determine the position of one side of the circulation cell. Where prominent
points of land interrupt the predominant longshore current flow, currents opposite
in direction are likely to develop in the current lee of the point (Shepard and Inman,
1960).
San Francisco Bay Estuary
San Francisco Bay is a complex estuary that is in part a Type B estuary which
at certain seasons assumes characteristics of a Type A or Type C estuary. It con
sists of many interconnected embayments, rivers, marshes, and sloughs (FIGURE 1).
This estuarine system is unusual in that it consists of two hydrodynamically and
geographically distinct reaches, the norther reach which includes the area south
and westward from the Delta to the Golden Gate, and the southern reach which extends
from the San Francisco-Oakland Bay Bridge south to San Jose. The waters of the
San Francisco Bay are a combination of ocean, river, and effluent discharges. The
- 57 -
SAN FRANCISCO BAY
1J* »^/*J B.CUI
FIGURE 1. The San Francisco Bay-Delta System.
Source: Conomos, 1979.
ratios of these waters and their compositions are continually changing depending on
various factors, including amount of river flow, time of year, amount of waste
discharge, configuration of the estuary, winds, and tidal influence.
The principal river flow into the bay is from the Sacramento and San Joaquin
Rivers. The norther reach receives 90 percent of the mean annual river inflow and
24 percent of the total wastewater inflow into the bay. The variations in water
properties in the south bay are determined by water exchange from the north and
the ocean, and by waste inflow (76 percent of the total wastewater inflow) (Conomos,
1979) .
The basic circulation patterns in the bay are tidally induced and are rela
tively unchanging throughout the year (Conomos, 1979). Tides in the bay are mixed
and semi-diurnal; two low and two high tides occur each tidal day (24.84 hrs.).
The high tides are unequal in height, as are the low tides (Conomos, 1979). Within
the bay, the tides create reversing currents that are strongest in the channels and
- 58 -
weaker in the shoals. The nontidal currents are generated by winds and river flow
and are important in transporting dissolved and particulate substances into and
from the bay.
Methodology
This study consisted of measuring the speed and direction of surface water
currents for the area between the Berkeley Marina and the Emeryville Marina in the
central bay. Due to time constraints and technical difficulties, bottom currents
could not be measured, although they are important in the transportation of sediment.
To date, no detailed studies have been conducted on the circulation patterns in
the study area; our field study is thus a first attempt.
There are two general methods for directly measuring currents (von Arx, 1962).
Eulerian methods consist of measuring the flow of water past a fixed point using
a current meter which records the speed and direction of flow. Lagrangian methods
track a parcel of water in space and time using a tracer. Devices that can be
used as tracers are drift bottles, radio buoys, current poles, drogues, or floats.
The Lagrangian method of measuring currents was used for this study. Drogues
were used to track the parcel of water. The drogue consisted of a *-liter plastic
soda bottle filled with approximately 9 ounces (by volume) of dry sand as ballast.
Two yellow flags were taped together and inserted through a small hole in the
bottle cap. A 4J-inch length of fluorescent orange tape was fixed to the stem of
the flags for easier visibility. Most of the bulk of the drogue rode below the
surface of the water, away from the direct effects of the wind.
Studies were conducted on four days: February 26, March 6, March 12, and April
17, 1982. A small motorboat was used for following the drogues. Sextants were
used to locate drogue positions. Successive readings of drogue positions were
taken until the drogues were picked up just prior to beaching. Speed of drogues
for each study day are given in Appendix A, which also lists which drogues were
beached before being picked up, which drogues were not recovered, and which
traveled out of the study area. Two of the studies were conducted under ebb tide
conditions and two were conducted under flood tide conditions.
A number of problems occurred throughout the study. Almost all of the drogues
from the first study day were beached before being picked up. Consequently, the
time of beaching could not be recorded, and the time it took a drogue to reach the
beach from its last recorded position could not be determined. Several drogues
became lost and were not recovered. A number of drogues from the first study day
- 59 -
drifted south of the Emeryville Marina out of the study area (see Appendix).
Results
The weather was slightly overcast or clear on all four study dates. Winds
were variable, ranging from calm to about 13.5 knots. FIGURES 2 through 5 show
the placement of drogues and the direction of drogue movement. The following is
a brief summary of the results of this study.
Saturday,• February 17, 1982 (FIGURE 2): Thirty-five drogues were released
starting from about 9/10 of a mile from shore at H's Lordships restaurant to the
north tip of the Emeryville Marina. The first drogue was released at 9:10 a.m.,
one hour after low tide. Most of the drogues were picked up by the time high tide
occurred at 2:33 p.m. No wind data were taken for this day. The drogues moved
southeast into shore at about .40 knots. Those that reached the Emeryville break
water continued to move shoreward along the breakwater. There was a slight
tendency for the drogues to move in a counter-clockwise fashion as they headed
for shore.
Saturday, March 6, 1982 (FIGURE 3): Twenty-four drogues were released in a
line starting from Shorebird Park cove (see map, page vi) to a point about 200 yards
north of the Cutter Building at the Emeryville Marina. The wind was calm at the
start of the study. The first drogue was released shortly before high tide at
8:57 a.m. The drogues were picked up by 1:00 p.m.; low tide occurred at 3:45 p.m.
The drogues started heading northwest and then circled clockwise to head northeast
to shore. Those drogues in the Shorebird Park cove area tended to describe a
tighter clockwise pattern. Drogues farther from shore or obstructions generally
moved at about .32 knots; those in the cove area moved at about .2 knots.
Friday, March 12, 1982 (FIGURE 4): Sixteen drogues were released in a line
from H's Lordships restaurant to a point approximately two-thirds of a mile south
towards the Emeryville Marina. Low tide occurred at 7:34 a.m., and high tide
occurred at 1:57 p.m. The first drogue was set out at 9:17 a.m., approximately
halfway between low and high tide. All drogues were picked up by 12:30 p.m. Wind
speed at 9:46 a.m. was 6.5-8 knots. Wind speed at 12:42 p.m. was 7.5-9 knots from
the northwest. All drogues moved southeast to the shoreline in a slightly counter
clockwise fashion. The speed was about .34 knots. In general, the drogues moved
in the same direction as those in the study conducted on February 27.
- 60 -
FIGURE2.LocationofDrogueReleasesandPatternofMovementforFebruary27,1982.
NOTE:Drogueswithnotrackingpatternwerelostafterinitialreleaseortraveledoutofthestudyarea.
LEGEND
•Initialrelease
ARetrievedbeforebeached
•Lostaltarthitpoint♦Baachad
)0O00
l_III-TT--I-
:cco*xotaat
FIGURE3.LocationofDrogueReleasesandPatternofMovementforMarch6,1982.
-61-
FIGURE 4. Location of Drogue Releases and Pattern of Movement for March 12, 1982
*fV: wa: *-
tc (j
T
•» Lordships' 7 J 9 10 » 12 " 14 ,516 18 19 202122Restaurant 23 24
LEGEND
• Initial release
A Retrieved before beached
• Lost alter this point
4) Beached
KOI 0
l-l H 13=
tow ;«o feet
FIGURE 5. Location of Drogue Releases and Pattern of Movement for April 17, 1982.
- 62 -
-
Saturday, April 17, 1982 (FIGURE 5): Seven drogues were set out in a line
between the Brickyard peninsula and H's Lordships restaurant; twenty drogues were
then set out in a line from H's Lordships to a point two-thirds of the way to the
Emeryville Marina. High tide occurred at 6:14 a.m., and low tide occurred at
1:15 p.m. The first drogue was released at 9:30 a.m., about halfway between the
high and low tides. All drogues were picked up by the beginning of the low tide.
Wind speed was 2.7-5.4 knots from the southwest at 8:50 a.m. Wind speed was
10.8-13.5 knots from the west at 1:30 p.m. The drogues at first moved northeast
to shore in a slightly clockwise motion and then moved due east straight in to
shore. The average speed was about .2 knots.
Discussion
Surface currents in the study area are affected by the tides and winds. It
was not possible to determine the effects of each separately; consequently, the
speed and direction measurements of the drogues represent a net circulation pattern.
In order to put together a comprehensive picture of water circulation patterns
in an area, studies should be conducted under different climatic conditions,
seasons, tidal cycles, and wind directions and speeds. Due to time constraints,
my study could only be conducted under different tidal cycles. Consequently, it
should be kept in mind that results from these studies apply only to this limited
situation. It is also desirable to map out a grid system for an initial release
of drogues at predetermined spots and reoccupy those stations at different study
dates in order to compare results from different studies. This was not possible
to do; using sextants to locate a predetermined position is extremely difficult and
time consuming. But for comparison of general circulation patterns, the additional
variable of different initial drogue release positions may not be very significant.
Regardless of the part of the tidal cycle during which the study was conducted,
all drogues moved shoreward; no drogues moved seaward. In general, when the tide
was moving in, the drogues moved southeast to the shore. When the tide was going
out, the drogues moved northeast to shore. In the more open areas of the embay-
ment, the drogues described a very slight clockwise or counter-clockwise tendency.
In the more confined areas, the drogues described tighter circular patterns. It
appears that the drogues moved faster when the tide was coming in than going out.
In addition, many drogues moved faster the closer they came to shore.
The surface currents were moving slowly. There was a tendency for wind stress
on the water surface, which had an effect on the direction of the surface currents
63 -
(Pirie, pers. comm., 1982). On the days of this study, surface water circulation
probably had little effect on sediment movement. Waves will have a much greater
effect on sediment movement than the currents (see paper by Peter Gee).
Conclusion
Before a beach can be established in this study area, it will be essential
to undertake numerous additional studies—my particular effort was just a beginning.
Bottom currents, especially, need to be studied. While the embayment is somewhat
sheltered and at a distance from the Sacramento and San Joaquin Rivers, it is
conceivable that there could be some river water influence on the currents in this
area. Studies could also be conducted on the possible influence of storm drain
and creek outflow that drain directly into the area; the movement of longshore
currents also needs to be studied. In addition, more detailed studies of the cir
culation around the Brickyard peninsula and other obstructions should be done.
Sediment movement is a complex process that is affected by many factors, of
which water circulation is only one. Under different physical conditions, or time
of year, different results may be obtained, with different conclusions reached.
Acknowledgments
I would like to thank Peter Gee and Don Bachman for their help in conducting
these studies; Douglas M. Pirie and George W. Domurat of the U.S. Army Corps of
Engineers for their help in setting up this study and interpretation of results;
and QMC R.W. Scott of U.C. Berkeley's Department of Naval Science for the use of
the sextants.
REFERENCES CITED
Bird, E.C.F.. 1968. Coasts: Canberra, Australian National University Press, 246 pp.
Conomos, T.J., 1979. Properties and Circulation of San Francisco Bay Waters,pp. 47-84 in Conomos, T.J., ed., San Francisco Bay, the Urbanized Estuary,Am. Assoc. Adv. of Sci., San Francisco, CA, 493 pp.
Johnson, Douglas Wilson, 1965. Shore Processes and Shoreline Development: NewYork, Hafner Publishing Company, 584 pp.
McCulloch, D.S., D.H. Peterson, P.R. Carlson, and T.J. Conomos, 1970. A PreliminaryStudy of the Effects of Water Circulation in the San Francisco Bay Estuary:U.S. Geological Survey Circular 637-A, B, 34 pp.
Pirie, Douglas M., Coastal Engineer, U.S. Army Corps of Engineers. Personalcommunication. May 19, 1982.
Pritchard. D.W., 1955. Estuarine Circulation Patterns: Proc. Am. Soc. CivilEng., v. 81, Separate No. 717, 427 pp.
- 64 -
-
I
r
•
r
REFERENCES CITED
(continued)
Pritchard, D.W., 1967. What Is an Estuary: Physical Viewpoint, pp. 3-5 in Lauff,George H., ed., Estuaries, Amer. Assoc. Adv. of Sci., Pub. No. 83, Washington,D.C. 757 pp.
Pritchard, D.W. and H.H. Carter, 1971. Estuarine Circulation Patterns, pp. IV-1to IV-17 iri Schubel, J.R., ed. , The Estuarine Environment, American Geological Institute, Washington, D.C, 339 pp.
Shepard, F.P. and D.L. Inman, 1950. Nearshore Circulation: Proc, First CoastalEng. Conf. Univ. Calif., 1950, pp. 50-59.
von Arx, William S., 1962. An Introduction to Physical Oceanography: Reading,Massachusetts, Addison-Wesley Publishing Company, Inc., 422 pp.
- 65 -
Drogue #
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
APPENDIX
DROGUE TRACKING TABLE
Speed (Knots)
Pt. 1 Pt. 2 Pt. 3 Pt. 4
to to to to
Pt. 2 Pt. 3 Pt. 4 Pt. 5
•.45
.44
.47
.39
.49
.23 .23
.26
.20
28
.30 .27
.29 36 .27
28 .41 .32
42 .40
56
,50
.54
.51
.54
52
.51
52
- 66 -
DATE: February 27, 1982
Comments
Lost after Pt. 2
Beached after Pt. 2
Lost after Pt. 2
Beached after Pt. 2
Beached after Pt. 2
Beached after Pt. 3
Lost after initial release
Lost after initial release
Traveled out of study area
Traveled out of study area
Traveled out of study area
Traveled out of study area
Traveled out of study area
Traveled out of study area
Traveled out of study area
Lost after initial release
Lost after initial release
Beached after Pt. 2
Beached after initial release
Lost after Pt. 2
Lost after Pt. 2
Beached after Pt. 3
Beached after Pt. 4
Beached after Pt. 4
Beached after Pt. 3
Beached after Pt. 2
Beached after Pt. 2
Beached after Pt. 2
Beached after Pt. 2
Beached after Pt. 2
Lost after after Pt. 2
Beached after Pt. 2
Beached after Pt. 2
Beached after Pt. 2
1
"
APPENDIX
DROGUE TRACKING TABLE
DATE: March 6, 1982
Speed (Knots)
'.
Drogue #
1
Pt. 1
to
Pt. 2
.10
Pt . 2
to
Pt. 3
Pt. 3
to
Pt. 4
Pt. 4
to
Pt. 5 Comments
p .23 _ -Beached after Pt. 3
2 .10 .22 _ -Beached after Pt. 3
3 .08 _ _ -Beached after Pt. 2
4 .14 .24 _ -Beached after Pt. 3
5 .20 .19 _ -Beached after Pt. 3
m6 .23 .21 _ -
Lost after Pt. 3
7 .26 .21 - -
Beached after Pt. 3
8 .28 .22 _ -
Beached after Pt. 3
• 9 .29 .26 _ -Beached after Pt. 3
10 .31 .23 — -Beached after Pt. 3
11 .34 .22 _ -
Beached after Pt. 3
I12 .36 .21 _ -
Beached after Pt. 3
f 13 .37 .25 _ -
Beached after Pt. 3
14 .36 .28 _ -
Beached after Pt. 3
f"15 .37 .31 _ -
Beached after Pt. 3
16 .38 .32 _. -Lost after Pt. 3
17 .40 .33 - -
Lost after Pt. 3
P»
18 .36 .36 _ -
Lost after Pt. 3
19 .31 .37 _ -
Beached after Pt. 3
20 .26 .37 _ -
Beached after Pt. 3
; 21 .17 .32 _ -Beached after Pt. 3
i
22 .08 .18 _ -
Lost after Pt. 3
— 23 .09 .14 _. -Beached after Pt. 3
24 .02 - --
Lost after Pt. 2
- 67 -
APPENDIX
DROGUE TRACKING TABLE
DATE: March 12, 1982
(Speed (Knots)
Drogue #
Pt. 1
Pt. 2
Pt. 2
Pt. 3
Pt. 3
Pt. 4
Pt. 4
Pt. 5 Comments
1 .54 .47 .25 _
Retrieved at Pt. 4
2 .53 .45 .23 _
Retrieved at Pt. 4
3 .55 .43 .25 _
Retrieved at Pt. 4
••] .18 .17 .21 .15 Retrieved at Pt. 5
5 .21 .19 .23 .18 Retrieved at Pt. 5
6 .20 .26 .27 .20 Retrieved at Pt. 5
7 .25 .32 .27 .21 Retrieved at Pt. 5
8 .45 .50 .26 _
Retrieved at Pt. 4
9 .56 .40 .22 _
Retrieved at Pt. 4
10 .55 .41 .20 _
Retrieved at Pt. 4
11 .51 .40 _ _
Retrieved at Pt.
at Pt.
3
12 .55 .38 .26 _
Retrieved 4
13 .53 .35 .28 _ Retrieved at Pt. 4
14 .53 .34 .26 _ Retrieved at Pt. 4
15 .52 .33 .25 ._
Retrieved at Pt. 4
16 .46 .34 .20- Retrieved at Pt. 4
- 68 -
n
r
>—
APPENDIX
DROGUE TRACKING TABLE
DATE: April 17, 1982
Speed (Knots)
Drogue # Pt. 2 Pt . 3 Pt. 4 Pt. 5 Comments
1 .22 - _ _ Beached after Pt. 2
2 .21 _ _ _ Beached a rter Pt. 2
3 .22 — _ _ Beached a fter Pt. 2
4 .15 . 15 _ _ Retrieved at Pt. 3
5 .15 — _ _ Retrieved at Pt. 2
6 .20 .19 _ _ Retrieved at Pt. 3
7 .18 .19 _ _ Retrieved at Pt. 3
8 .20 .18 _ _ Retrieved at Pt. 3
9 .23 .22 _ _ Retrieved at Pt. 3
10 .20 .21 _ _ Retrieved at Pt. 3
11 .17 .20 - _ Retrieved at Pt. 3
12 .20 .25 _ _ Lost after Pt. 3
13 .20 .24 .27 _ Retrieved at Pt. 4
14 .17 .21 .27 _ Retrieved at Pt. 4
15 .16 .18 .26 _ Retrieved at Pt. 4
16 .21 .24 .23 _ Retrieved at Pt. 4
17 .18 .23 _ _ Beached after Pt. 3
18 .21 .19 .27 _ Retrieved at Pt. 4
19 .17 .22 .29 _ Retrieved at Pt. 4
20 .18 .11 .26 _ Retrieved at Pt. 4
21 .14 . 19 .41 _ Retrieved at Pt. 4
22 .15 .16 .24 _ Retrieved at Pt. 4
23 .14 .23 .24 _ Retrieved at Pt. 4
24 .17 .20 .28 _ Retrieved at Pt. 4
25 .11 .16 .25 _ Retrieved at Pt. 4
26 .14 .19 .26 _ Retrieved at Pt. 4
27 .06 .13 .21 - Retrieved at Pt. 4
- 69 -